Autoimmune diseases occur when an organism's immune system fails to recognize some of the organism's own tissues as “self” and attacks them as “foreign.” Normally, self-tolerance is developed early by developmental events within the immune system that prevent the organism's own T cells and B cells from reacting with the organism's own tissues. MHC cell surface proteins help regulate these early immune responses by binding to and presenting processed peptides to T cells.
This self-tolerance process breaks down when autoimmune diseases develop. Now the organism's own tissues and proteins are recognized as “autoantigens” and are attacked by the organism's immune system. For example, multiple sclerosis is believed to be an autoimmune disease occurring when the immune system attacks the myelin sheath, whose function is to insulate and protect nerves. It is a progressive disease characterized by demyelination, followed by neuronal and motor function loss. Rheumatoid arthritis (“RA”) is also believed to be an autoimmune disease which involves chronic inflammation of the synovial joints and infiltration by activated T cells, macrophages and plasma cells, leading to a progressive destruction of the articular cartilage. It is the most severe form of joint disease. The nature of the autoantigen(s) attacked in rheumatoid arthritis is poorly understood, although collagen type II is a candidate.
A tendency to develop multiple sclerosis and rheumatoid arthritis is inherited—these diseases occur more frequently in individuals carrying one or more characteristic MHC class II alleles. For example, inherited susceptibility for rheumatoid arthritis is strongly associated with the MHC class II DRB1 *0401, DRB 1 *0404, or DRB 1*0405 or the DRB1*0101 alleles. The histocompatibility locus antigens (HLA) are found on the surface of cells and help determine the individuality of tissues from different persons. Genes for histocompatibility locus antigens are located in the same region of chromosome 6 as the major histocompatibility complex (MHC). The MHC region expresses a number of distinctive classes of molecules in various cells of the body, the genes being, in order of sequence along the chromosome, the Class I, II and III MHC genes. The Class I genes consist of HLA genes, which are further subdivided into A, B and C subregions. The Class II genes are subdivided into the DR, DQ and DP subregions. The MHC-DR molecules are the best known; these occur on the surfaces of antigen presenting cells such as macrophages, dendritic cells of lymphoid tissue and epidermal cells. The Class III MHC products are expressed in various components of the complement system, as well as in some non-immune related cells.
A number of therapeutic agents have been developed to treat autoimmune diseases, including steroidal and non-steroidal anti-inflammatory drugs, for example, methotrexate; various interferons; and certain inhibitors of prostaglandin synthesis. However, these agents can be toxic when used for more than short periods of time or cause undesirable side effects. Other therapeutic agents bind to and/or inhibit the inflammatory activity of tumor necrosis factor (TNF), for example, anti-TNF specific antibodies or antibody fragments, or a soluble form of the TNF receptor. These agents target a protein on the surface of a T cell and generally prevent interaction with an antigen presenting cell (APC). However, therapeutic compositions containing natural folded proteins are often difficult to produce, formulate, store, and deliver. Moreover, the innate heterogeneity of the immune system can limit the effectiveness of drugs and complicate long-term treatment of autoimmune diseases.
Thus in order to effectively treat autoimmune diseases and other immune conditions, new drugs are needed that do not have the side effects of the present therapeutic agents and which adequately address to the innate heterogeneity of the immune system.